Can REEs be green chemistry?

Rare earths, critical elements, lanthanides, by any name are just as vital

In the green chemistry space, it’s not uncommon to focus on petrochemicals - chemicals made of carbon and hydrogen (hydrocarbons) that come from fossil fuels. With the coming shift to renewable resources, and today’s boom in biotechnology, moving away from petrochemicals is a natural and important target. So often when I say I work with sustainable chemicals, people think of plastics and surfactants.

But there are other types of chemicals. A lesser-known side of green chemistry is working with inorganic (non-hydrocarbon) chemicals, like clays and metals. We’ve recently started working on a grant-funded project in rare earth elements (REEs), and it’s been a fascinating area to explore.

If you’re not familiar (and probably you’re not!), REEs are hugely important to a high-tech sustainable society. We need them for electric vehicles, wind turbines, and even cell phones. There are 17 of these elements on the periodic table—the 15 lanthanides, plus scandium and yttrium. Their unique properties make them impossible to replace, and since the current rate of recycling is effectively zero, there’s a mad scramble going on between global powers to grab the resources for themselves. Academics are studying how to mine REEs from new sources, like the deep sea, and even the moon.

Of course, mining from the deep sea (or the moon) is not likely to be a sustainable process. Neither are the methods we use now to get REEs from the earth, which include open pit mining. Once the ore is collected, the REEs are often extracted using strong acids and temperatures of 400-500°C, and then refined using repeated solvent extractions—sometimes over 1,800 extractions to get to the high purity level needed.

So that’s not very green.

How can we do better? In particular, how can the UK, with no REE reserves to speak of, compete with China, which holds a full third of the global REE reserves and is taking great pains to capitalise on them?

The answer probably will not surprise you—build a circular economy! Or industrial symbiosis, or waste valorisation, or whatever your preferred term is for recovering and reusing valuable bits from waste streams. In short, we need to recycle REEs.

This recycling stream is particularly interesting because it’s not driven by sustainability, but by unavoidable need (and profit). It’s a matter of national security, so government support is not likely to be affected by political shenanigans. Long-term support looks likely, which is exactly the kind of confidence needed to unlock private investment.

And so, research and commercialisation in this field is booming. A truckload of UK- and EU-funded research projects have been looking at how to better track and collect REE waste, how to break it apart and recover the REEs, and how to then purify those REEs for reuse. How can green chemistry help?

In our project, we’re looking at safer solvents and greener processes. Can ionic liquids remove the need for strong acids, high temperatures, and thousands of repeat extractions? Can smarter chemistry cut out some of the processing steps altogether? Or pull REEs out of waste streams previously thought to be useless? And if the technology works, where exactly can it add the most value?

That last bit is always a crucial question, as new chemical technologies usually can’t compete with the massive economies of scale achieved by bulk chemical processes. We’ll be working to identify the potential for this technology to create value for customers, so it doesn’t have to rely on its green credentials to make the sale. For me, that’s the most obvious way forward—work with the current of capitalism to bring positive change about.